Photonic crystals (PhCs), the optical analogues of electronic semiconductors, have been the subject of intense international research efforts for well over a decade. A photonic crystal consists of an ordered dielectric structure having a spatially periodic dielectric constant with a lattice constant comparable to, or less than, the wavelength of the electromagnetic wave. A photonic crystal with a complete band gap can be used to localize electromagnetic waves, inhibit spontaneous emission, and to guide the propagation of electromagnetic waves along certain directions. Due to the performance enhancement they provide in terms of emission control, guiding, and dispersion engineering, PhCs are expected to become the elementary building blocks of next-generation opto-electronic devices.
A complete band gap in the microwave regime has previously been demonstrated. However, the fabrication of 3D photonic crystals for other regions of the electromagnetic spectrum continues to be a challenging problem. Currently, some of the more popular fabrication methods pursued actively in the research community fall generally into three categories: layer-by-layer; fabrication; interferometric and multi-photon volumetric lithography, and self-assembly techniques.
Each of these categories possesses unique advantages and disadvantages. Most layer-by-layer methods realize PhCs directly in high-index dielectrics and semiconductors, but require tedious repetitive alignment, patterning, etching and deposition cycles. Self-assembly methods can quickly realize large-volume 3D PhCs, but they tend to contain many unintended defects and must be back-filled with high-index material to obtain a complete gap. Multi-photon absorption patterning can produce quality PhCs with designed defects, but they are serial in nature and thus poorly suited to batch fabrication, and like self-assembly they yield low index-contrast PhCs.
What is needed is a lithographic approach for producing PhCs that is compatible with existing semiconductor microelectronics fabrication techniques, e.g., lithographic techniques.